1. Field of the Invention
This invention relates to a magnetic recording medium having a metamorphosed layer on the magnetic layer to prevent emergence of sticky material from the magnetic layer, a process for producing the same, a method for treating the surface of a magnetic recording medium so as to prevent sticking trouble between a magnetic head and the magnetic recording medium, and an apparatus for conducting such a treatment.
2. Description of the Prior Art
Magnetic tapes used as magnetic recording medium in magnetic tape recording equipments, magnetic tape recoders, and the like have structure as shown in the attached FIG. 1 wherein a magnetic layer 2 obtained by dispersing magnetic particles in a binder is adhered to a base film 1 such as polyethylene terephthalate film. These magnetic tapes are usually produced by the steps as shown in FIG. 2. That is, magnetic particles are mixed with a binder, a solvent and other additives for dispersion and the resulting coating dispersion is filtered before coating with, for example, a roll coater. On the other hand, a base film previously washed is led to the roll coater and the coating dispersion is coated on the base film at a speed of, for example, about 6 m/min. After the coating step, a magnetic field is applied to the resulting coating, if necessary to the coating direction, to impart magnetic orientation (orientation step). Subsequently, the solvent is evaporated in a high-temperature drying step, e.g. at about 120.degree. C. for 2 minutes. If it is necessary to smooth the surface of the resulting magnetic layer, the magnetic layer is subjected to a surface treatment step by using a calender roll conventionally used to smooth the surface. The resulting tape is slitted to a prescribed size and then subjected to testing and packaging steps not shown in FIG. 2 to give commercially available magnetic tapes.
When these conventional magnetic tapes thus produced are used practically in magnetic tape recording equipments, magnetic tape recorders, and the like, there often occurs sticking phenomenon of the magnetic tape on a magnetic head which reads on signals depending on travel and stoppage of the magnetic tape. That is, when the magnetic tape is stopped after travel of a certain distance and starts travel again after some intervals, there occasionally occurs a trouble of not moving the magnetic tape due to sticking of the magnetic tape to the magnetic head. Hereinafter such a trouble is referred to as sticking trouble.
Heretofore, there has been almost no systematic report on the sticking trouble except for an article "A Sudy of Frictional and Stick-Slip Behavior of Magnetic Recording Tapes " by S. H. Kalfayer, R. H. Silver and J. K. Hoffman--NASA Technical Report 32-1548 (published Apr. 1, 1972). But there is no description as to fundamental countermeasure for preventing the sticking trouble in said article and there is disclosed only an idea of keeping magnetic tapes at low temperatures for preventing the sticking trouble with some effect.
Contrary to such a poor countermeasure for preventing the sticking trouble, there is a great need for urgent development of a technique for preventing the sticking trouble taking the output and using amount of magnetic tapes into consideration. Magnetic tapes conventionally used have many chances of suffering the sticking trouble except for special kinds of magnetic tapes.
The present inventors extensively studied to remove such a defect of magnetic tapes and found that no remarkable effects were obtained by a heating treatment wherein the temperature of the tape is raised, a treatment under high humidity, a radiation treatment, washing with chemicals, a treatment by irradiating light or infrared rays. When an isocyanate which is known as an urethane curing accelerator was used, considerable effect was obtained but there was also produced an undesirable side effect of extension of one-side of the magnetic tape; such a treatment cannot be used practically. Only a treatment with ultraviolet rays was effective and the present invention was accomplished.